1. Field of the Invention
The present invention relates to a technology of controlling a magnetic disc storage apparatus, in details, to a technology of controlling a voice coil motor for moving a magnetic head for reading/writing information to and from a storage track on a magnetic storage disc driven to spin.
2. Description of the Related Art
A magnetic disc storage apparatus includes a magnetic head for reading/writing information to and from a storage track on a magnetic storage disc driven to spin, a voice coil motor for moving the magnetic head above a disc and a magnetic head driving system for carrying out position control of the magnetic head by controlling driving current of the voice coil motor by a feedback control while monitoring a state of reading of the magnetic head.
An information recording density of a magnetic disc storage apparatus has been increased year by year and in accordance therewith, very high accuracy has also been requested for position control of a magnetic head. Therefore, in driving a voice coil motor of moving the magnetic head, there is adopted a linear drive system for continuously changing an amount of driving current of the voice coil motor.
However, it has been clarified by the inventors that the following problem is posed in the above-described technology.
That is, according to a magnetic disc storage apparatus, with high density formation of storage, high speed formation of access is also requested. Although in order to realize high speed access, a time period of moving the magnetic head to a predetermined storage track, so-to-speak seek time, must be shortened, for such purpose, driving current of the voice coil motor needs to increase.
However, when the driving current of the voice coil motor is increased, power dissipation for linearly controlling the driving current is increased and a heating amount is increased in accordance therewith. The heating in seeking effects adverse influence on operation and characteristics of the magnetic head and the magnetic storage disc, thereby, for example, there causes a drawback that read/write error is liable to produce.
Hence, in order to alleviate the heating, the inventors have investigated to control the driving current of the voice coil motor by pulse width modulation (PWM) control. That is, the inventors have investigated a pulse drive system for controlling to drive the voice coil motor not by continuously changing an amount of the driving current of the voice coil motor but by changing a ratio of driving period vs non-driving period of the driving current. In this case, the voice coil motor is controlled to drive by fixing the amount of the driving current of the voice coil motor to a vicinity of a maximum value thereof and changing the ratio of driving period vs non-driving period.
However, it has been clarified that there poses a problem that although the pulse drive system is effective in restraining the heating amount by reducing power dissipation, in comparison with the above-described linear drive system, it is difficult to sufficiently ensure control accuracy, particularly, positioning accuracy of the magnetic head in tracking when an amount of moving the magnetic head is small, EMI (electromagnetic interference) noise produced in accordance with pulse control of the driving current, jumps into the magnetic head and there is a high possibility of inducing read error of a hard disk drive.